In the past, there has been known a stern tube sealing device which is formed in a stern tube for rotatably supporting a propeller shaft of a marine vessel, and seals an outer periphery of the propeller shaft (for example, refer to a first patent literature). A stern tube sealing device according to a conventional example will be explained while referring to FIG. 4. FIG. 4 is a view showing the schematic construction of the stern tube sealing device according to the conventional example.
In the stern tube sealing device 400 according to this conventional example, a first seal ring chamber 411 and a second seal ring chamber 412 are formed in a seal housing 410 through which a propeller shaft 200 is inserted. The second seal ring chamber 412 is located at an inboard side of the first seal ring chamber 411.
A first seal ring 421 is arranged in the first seal ring chamber 411. A second seal ring 422 is arranged in the second seal ring chamber 412. The first seal ring 421 and the second seal ring 422 are fixedly secured to the propeller shaft 200, so that they rotate together with the propeller shaft 200. In addition, the first seal ring 421 has a sealing surface 421a which is in contact with an inboard side wall surface in the first seal ring chamber 411 so as to slide with respect to the wall surface. The second seal ring 422 has an inboard side sealing surface 422a which is in contact with an inboard side wall surface in the second seal ring chamber 412 so as to slide with respect to the wall surface.
The first seal ring chamber 411 is in communication with an outside of the marine vessel. In addition, the first seal ring chamber 411 and the second seal ring chamber 412 are in communication with each other through sliding portions of the wall surface of the first seal ring chamber 411 and the sealing surface 421a of the first seal ring 421.
In this stern tube sealing device 400, sealing is exhibited by maintaining a state in which at least either one of the sealing surfaces 421a, 422a of the first seal ring 421 and the second seal ring 422 is in intimate contact with the inboard side wall surface of the first seal ring chamber 411 or the second seal ring chamber 412.
Further, sea water SW is introduced into the individual insides of the first seal ring chamber 411 and the second seal ring chamber 412 through a first sea water introduction pipe 431 and a second sea water introduction pipe 432, respectively. As a result of this, the individual seal rings 421, 422 can be cooled with the sea water which is filled in each of the seal ring chambers 411, 412.
However, in cases where slurry is mixed in the sea water SW, when the sea water SW is introduced into the seal ring chambers 411, 412, there will be a fear that the slurry may come into the sliding portions between the sealing surfaces 421a, 422a of the individual seal rings 421, 422 and the wall surfaces of the individual seal ring chambers 411, 412. When the slurry having come into these sliding portions deposits on the sliding portions, there will occur a problem that sealing efficiency is decreased. In addition, another problem will also occur in which the wall surfaces of the seal ring chambers 411, 412 wear due to the slurry.
Here, note that in cases where the construction of the stern tube sealing device is such that each seal ring is fixedly secured to a seal housing side in each seal ring chamber, with the sealing surface of each seal ring being slidable while being in contact with the outer peripheral surface of the propeller shaft, too, when the sea water with the slurry mixed therein is introduced into each seal ring chamber, the slurry may come into the sliding portions of the sealing surface of each seal ring and the outer peripheral surface of the propeller shaft. In this case, too, the deposition of the slurry on the sliding portions causes a problem that sealing efficiency is decreased, and another problem that the wall surface of the propeller shaft wears due to the slurry.
In addition, the problems as mentioned above can of course occur, not only in cases where sea water is introduced into the seal ring chambers, but also in cases where water (i.e., outboard water) such as in rivers, etc., is introduced into seal ring chambers in a stern tube sealing device in a marine vessel used in rivers or the like, if slurry is mixed in the water such as river water.